Method for communicating in wireless communication system supporting multiple access network and apparatus supporting same

ABSTRACT

Provided is a method for communicating performed by a terminal in a wireless communication system. The method comprises receiving a traffic routing configuration from a first access network, the traffic routing configuration specifying a traffic routing criteria for routing and processing traffic, discovering at least one second network entity by searching a second access network, conducting a traffic routing evaluation to determine whether the at least one second access network satisfies the traffic routing criteria, reporting a routing evaluation result to the first access network when the traffic routing criteria are satisfied, receiving a traffic routing indication from the first access network, and processing the traffic based on the traffic routing indication. When the traffic routing indication indicates traffic of the first access network is processed through the second access network, the traffic of the first access network is processed through the second access network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2013/011907, filed on Dec. 19, 2013, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/739,705,filed on Dec. 19, 2012, all of which are hereby expressly incorporatedby reference into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a communication method performed in a wirelesscommunication system supporting communication through a multiple accessnetwork and an apparatus supporting the same.

2. Related Art

3GPP (3rd Generation Partnership Project) LTE (long term evolution)which is improvement of UMTS (Universal Mobile TelecommunicationsSystem) has been introduced as 3GPP release 8. The 3GPP LTE uses OFDMA(orthogonal frequency division multiple access) in a downlink, and usesSC-FDMA (Single Carrier-frequency division multiple access) in anuplink. The 3GPP LTE adopts MIMO (multiple input multiple output) havingmaximum four antennas. Recently, a discussion of 3GPP LTE-A(LTE-Advanced) which is the evolution of the 3GPP LTE is in progress.

The wireless communication system can support providing a servicethrough a plurality of access networks to the terminal. The terminal canreceive the service from a 3GPP based access network such as a mobilewireless communication system and further, receive a service fromnon-3GPP based access networks such as Worldwide Interoperability forMicrowave Access (WiMAX), Wireless Local Area Network (WLAN), and thelike.

Interworking between the 3GPP access network and the non-3GPP accessnetwork in the related art is a scheme in which the terminal selects theaccess network based on an access network discovery and selectionfunctions (ANDSF) policy and processes traffic through the selectedaccess network. In this scheme, a base station cannot control theinterworking between the 3GPP access network and the non-3GPP accessnetwork. This cannot properly allocate a radio resource to the terminalthat receives a service in a cell to cause a problem in that a qualityof service (QoS) of the terminal deteriorates.

SUMMARY OF THE INVENTION

The present invention provides a method for communicating in a wirelesscommunication system supporting a multiple access network and anapparatus supporting the same.

In an aspect, provided is a method for communicating carried out by aterminal in a wireless communication system supporting a multiple accessnetwork. The method includes receiving a traffic routing configurationfrom a first access network, the traffic routing configurationspecifying a traffic routing criterion for routing and processingtraffic, searching a second access network to discover at least onesecond access network entity, performing traffic routing evaluationdetermining whether at least one second access network entity satisfiesthe traffic routing criterion, reporting a routing evaluation result tothe first access network when the traffic routing criterion issatisfied, receiving a traffic routing indication from the first accessnetwork and processing the traffic based on the traffic routingindication. When the traffic routing indication indicates that trafficof the first access network is processed through the second accessnetwork, in the processing of the traffic based on the traffic routingindication, the traffic of the first access network is processed throughthe second access network.

The traffic routing indication may indicate the second access networkentity for processing the traffic of the first access network. Thetraffic of the first access network may be processed by the secondaccess network entity indicated by the traffic routing indication.

The routing evaluation result may include at least one of identificationinformation indicating at least one entity satisfying the trafficrouting criterion among at least one second access network entities,channel information of at least one entity satisfying the trafficrouting criterion and information on the first access network traffic.

The second access network entity indicated by the traffic routingindication may be selected by the first access network among at leastone entity indicated by the identification information of the routingevaluation result.

The information on the first access network traffic may include a radiobearer identifier list associated with the first access network traffic.

The traffic routing indication may include an identifier indicating theindicated second access network entity, and traffic information ontraffic of which processing through the indicated second access networkentity is permitted.

The traffic information may include a radio bearer identifier listassociated with the traffic of which processing through the indicatedsecond access network entity is permitted.

The processing of the traffic of the first access network may includeprocessing the traffic indicated by the traffic information of thetraffic routing indication among the traffic of the first access networkthrough the target second access network entity.

The traffic routing configuration may include a routing entity listincluding at least one second access network entity in which the trafficprocessing of the first access network is permitted.

The performing of the traffic routing evaluation may include deciding,when the second access network entity discovered by the search isincluded in the routing entity list, that the corresponding secondaccess network entity satisfies the traffic routing criterion.

The method may further include: reporting a result of the trafficprocessing of the first access network to the first access network.

The method may further include: releasing a radio resource control (RRC)connection with the first access network after reporting the firstaccess network traffic processing result.

The method may further include: receiving traffic processingconfirmation from the first access network as a response to the firstaccess network traffic processing result reporting and releasing the RRCconnection with the first access network when the traffic processingconfirmation indicates that the first access network traffic is normallyprocessed.

When the traffic routing indication indicates that traffic of the secondaccess network is processed through the first access network, theprocessing of the traffic based on the traffic routing indication mayinclude processing the traffic of the second access network through thefirst access network.

The first access network may be a 3rd generation partnership project(3GPP) based access network, and the second access network is a wirelesslocal area network (WLAN) based access network.

In another aspect, provided is a wireless apparatus that operates in awireless communication system. The wireless apparatus includes a firstRF unit transmitting and receiving a first access network signal, asecond RF unit transmitting and receiving a second access networksignal, a processor that operates in functional combination with thefirst RF unit and the second RF unit. The processor is configured toreceive a traffic routing configuration from a first access network, thetraffic routing configuration specifying a traffic routing criterion forrouting and processing traffic, search a second access network todiscover at least one second access network entity, perform trafficrouting evaluation determining whether at least one second accessnetwork entity satisfies the traffic routing criterion, report a routingevaluation result to the first access network when the traffic routingcriterion is satisfied, receive a traffic routing indication from thefirst access network, and process the traffic based on the trafficrouting indication, and when the traffic routing indication indicatesthat traffic of the first access network is processed through the secondaccess network, the processing of the traffic based on the trafficrouting indication includes the traffic of the first access networkthrough the second access network.

According to the communication method of the embodiment of the presentinvention, in the interworking between the 3GPP access network and thenon-3GPP access network, the base station of the 3GPP access network cancontrol the interworking. The base station controls the operation of theterminal with a control right for the terminal to control the loads ofthe core network and the radio link. Therefore, the base station cansatisfy the terminal that receives the service in the cell or the QoS ofthe specific traffic of the terminal by efficiently using the radioresource.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system to which the presentinvention is applied.

FIG. 2 is a block diagram illustrating a radio protocol architecture fora user plane.

FIG. 3 is a block diagram illustrating a radio protocol architecture fora control plane.

FIG. 4 is a flowchart illustrating an operation of the UE in the RRCidle state.

FIG. 5 is a flowchart illustrating a process of establishing RRCconnection.

FIG. 6 is a flowchart illustrating an RRC connection reconfigurationprocess.

FIG. 7 is a flowchart illustrating a handover process.

FIG. 8 is a diagram illustrating a RRC connection re-establishmentprocedure.

FIG. 9 is a diagram illustrating an example of an environment in whichthe 3GPP access network and the WLAN access network coexist.

FIG. 10 is a diagram illustrating a communication method according to anembodiment of the present invention.

FIG. 11 is a diagram illustrating an example of a communication methodaccording to an embodiment of the present invention.

FIG. 12 is a diagram illustrating one example of a communication methodaccording to an embodiment of the present invention.

FIG. 13 is a diagram illustrating another example of a communicationmethod according to an embodiment of the present invention.

FIG. 14 is a block diagram illustrating a wireless apparatus in whichthe embodiment of the present invention may be implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a wireless communication system to which the presentinvention is applied. The wireless communication system may be called anevolved-UMTS terrestrial radio access network (E-UTRAN), or a long termevolution (LTE)/LTE-A system.

The E-UTRAN includes a base station (BS) 20 which provides a controlplane and a user plane to user equipment (UE) 10. The UE 10 may be fixedor have mobility, and may be referred to as other terms such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), a mobileterminal (MT), and a wireless device. The BS 20 generally represents afixed station that communicates with the UE 10 and may be referred to asother terms such as an evolved-NodeB (eNB), a base transceiver system(BTS), and an access point.

The BSs 20 may be connected to each other through an X2 interface. TheBS 20 is connected with an evolved packet core (EPC) 30 through an S1interface, and more particularly, connected with a mobility managemententity (MME) through an S1-MME and a serving gateway (S-GW) through anS1-U.

The EPC 30 is constituted by the MME, the S-GW, and a packet datanetwork-gateway (P-GW). The MME has access information of the UE orinformation regarding capacity of the UE, and the information isfrequently used in mobility management of the UE. The S-GW is a gatewayhaving the E-UTRAN as an end point, and the P-GW is a gateway having thePDN as an end point.

Layers of a radio interface protocol between the UE and the network maybe divided into a first layer L1, a second layer L2, and a third layerL3 based on three lower layers of an open system interconnection (OSI)standard model which is widely known in the communication system, andamong them, a physical layer to which the first layer belongs providesan information transfer service using a physical channel, and a radioresource control (RRC) layer positioned on the third layer serves tocontrol a radio resource between the UE and the network. To this end,the RRC layer exchanges an RRC message between the UE and the network.

FIG. 2 is a block diagram illustrating a radio protocol architecture fora user plane. FIG. 3 is a block diagram illustrating a radio protocolarchitecture for a control plane. The user plane is a protocol stack foruser data transmission, and the control plane is a protocol stack forcontrol signal transmission.

Referring to FIGS. 2 and 3, a physical (PHY) layer provides aninformation transfer service to an upper layer by using a physicalchannel. The PHY layer is connected with a medium access control (MAC)layer which is the upper layer through a transport channel. Data movebetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how the data istransmitted through a radio interface with any characteristic.

The data move between different PHY layers, that is, the PHY layers ofthe transmitter and the receiver through the physical channel. Thephysical channel may be modulated by an orthogonal frequency divisionmultiplexing (OFDM) scheme, and use a time and a frequency as the radioresource.

A function of the MAC layer includes mapping between a logical channeland a transport channel and multiplexing/demultiplexing to a transportblock provided to the physical channel on the transport channel of a MACservice data unit (SDU) which belongs to the logical channel. The MAClayer provides a service to a radio link control (RLC) layer through thelogical channel.

A function of the RLC layer includes concatenation, segmentation, andreassembly of the RLC SDU. In order to secure various quality ofservices (QoS) required by a radio bearer (RB), an RLC layer providesthree operation modes of a transparent mode (TM), an unacknowledged mode(UM), and an acknowledged mode (AM). The AM RLC provides an errorcorrection through an automatic repeat request (ARQ).

The radio resource control (RRC) layer is defined only in the controlplane. The RRC layer is related with configuration, re-configuration,and release of the RBs to serve to control the logical channel, thetransport channel, and the physical channels. The RB means a logic pathprovided by a first layer (PHY layer) and a second layer (MAC layer, RLClayer, or PDCP layer) in order to transfer the data between the UE andthe network.

A function of a packet data convergence protocol (PDCP) layer in theuser plane includes transfer, header compression, and ciphering of theuser data. A function of the PDCP layer in the control plane includestransfer and ciphering/integrity protection of control plane data.

The configuration of the RB means a process of defining characteristicsof the radio protocol layer and the channel in order to provide aspecific service and configuring each detailed parameter and operationmethod. The RB may be divided into a signaling RB (SRB) and a data RB(DRB) again. The SRB is used as a path for transmitting an RRC messagein the control plane, and the DRB is used as a path for transportinguser data in the user plane.

When RRC connection is established between the RRC layer of the UE andthe RRC layer of the E-UTRAN, the UE is in an RRC connected state, andif not, the UE is in an RRC idle state.

A downlink transport channel for transporting the data to the UE fromthe network includes a broadcast channel (BCH) for transporting systeminformation and a downlink shared channel (SCH) for transporting usertraffic or a control message. The traffic or the control message of adownlink multicast or broadcast service may be transported through thedownlink SCH, or may be transported through a separate downlinkmulticast channel (MCH). Meanwhile, an uplink transport channel fortransporting the data from the UE to the network includes a randomaccess channel (RACH) for transporting an initial control message and anuplink shared channel (SCH) for transporting the user traffic or thecontrol message in addition to the RACH.

A logical channel which is above the transport channel and mapped in thetransport channel includes a broadcast control channel (BCCH), a pagingcontrol channel (PCCH), a common control channel (CCCH), a multicastcontrol channel (MCCH), a multicast traffic channel (MTCH), and thelike.

The physical channel is constituted by several OFDM symbols in a timedomain and several sub-carriers in a frequency domain. One sub-frame isconstituted by a plurality of OFDM symbols in the time domain. The RB asa resource allocation unit is constituted by a plurality of OFDM symbolsand a plurality of sub-carriers. Further, each sub-frame may usespecific sub-carriers of specific OFDM symbols (for example, first OFDMsymbols) of the corresponding sub-frame for the physical downlinkcontrol channel (PDCCH), that is, a L1/L2 control channel. Atransmission time interval (TTI) is a unit time of sub-frametransmission.

As disclosed in 3GPP TS 36.211 V8.7.0, a physical channel in 3GPP LTEmay be divided into the physical downlink shared channel (PDSCH) and aphysical uplink shared channel (PUSCH) which are data channels, and aphysical downlink control channel (PDCCH), a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), and a physical uplink control channel (PUCCH) which are datachannels.

The PCFICH transmitted in a first OFDM symbol of the subframe transportsa control format indicator (CFI) regarding the number (that is, the sizeof the control region) of OFDM symbols used to transmit control channelsin the subframe. The terminal first receives the CFI on the PCFICH andthereafter, monitors the PDCCH.

The PDCCH as a downlink control channel is also referred to as ascheduling channel in terms of transporting scheduling information.Control information transmitted through the PDCCH is called downlinkcontrol information (DCI). The DCI may include resource allocation (alsoreferred to as downlink (DL) grant) of the PDSCH, resource allocation(also referred to as uplink (UL) grant) of the PUSCH, a set oftransmission power control commands for individual UEs in apredetermined UE group, and/or activation of a voice over Internetprotocol (VoIP).

In 3GPP LTE, the terminal uses blind decoding in order to detect thePDCCH. The blind decoding is a scheme that checks a CRC error bydemasking a desired identifier to a CRC of a received PDCCH (referred toas a PDCCH candidate) to check whether the corresponding PDCCH is acontrol channel thereof.

The base station determines a PDCCH format according to a DCI to betransmitted to the terminal and then adds a cyclic redundancy check(CRC) to the DCI, and masks a unique identifier (referred to as a radionetwork temporary identifier (RNTI)) to the CRC according to an owner ora usage of the PDCCH.

Hereinafter, an RRC state of the UE and an RRC connection method will bedescribed.

The RRC state means whether the RRC layer of the UE is logical-connectedwith the RRC layer of the E-UTRAN or not, and a case where the RRC layerof the UE is connected with the RRC layer of the E-UTRAN is called a RRCconnection state, and a case where the RRC layer of the UE is notconnected with the RRC layer of the E-UTRAN is called an RRC idle state.Since the RRC connection exists in the UE in the RRC connection state,the E-UTRAN may determine the existence of the corresponding UE in acell unit, and as a result, the UE may be efficiently controlled. On theother hand, the UE in the RRC idle state may not be determined by theE-UTRAN, and a core network (CN) is managed by a tracking area unitwhich is a larger area unit than the cell. That is, in the UE in the RRCidle state, only the existence is determined by a large area unit, andthe UE needs to move in the RRC connection state in order to receive ageneral mobile communication service such as voice or data.

When the user first turns on the power of the UE, the UE first searchesa proper cell and then stays in the RRC idle state in the correspondingcell. The UE in the RRC idle state establishes the RRC connection withthe E-UTRAN through an RRC connection procedure only when the RRCconnection is required, and is transited into the RRC connection state.There are several cases where the UE in the RRC idle state requires theRRC connection, and for example, uplink data transmission is requireddue to reasons such as user's call attempt, or a response message to acase where a paging message is received from the E-UTRAN is transmitted.

A non-access stratum (NAS) layer positioned above the RRC layer performsfunctions such as a session management and a mobility management.

In the NAS layer, in order to manage mobility of the UE, two states ofEDEPS mobility management-REGISTERED (EMM-REGISTER) and EMM-DEREGISTEREDare defined, and the two states are applied to the UE and the MME. Theinitial UE is in the EMM-DEREGISTERED state, and the UE performs aprocedure of registering the UE in the corresponding network through aninitial attaching procedure so as to be connected to the network. Whenthe attaching procedure is successfully performed, the UE and the MMEare in the EMM-REGISTERED state.

In order to manage signaling connection between the UE and the EPS, twostates of an EPS connection management (ECM)-IDLE state and anECM-CONNECTED state, and the two states are applied to the UE and theMME. When the UE in the ECM-IDLE state is RRC-connected with theE-UTRAN, the corresponding UE becomes in the ECM-CONNECTED state. Whenthe MME in the ECM-IDLE state is S1-connected with the E-UTRAN, thecorresponding MME becomes in the ECM-CONNECTED state. When the UE is inthe ECM-IDLE state, the E-UTRAN does not have context information of theUE. Accordingly, the UE in the ECM-IDLE state performs a procedurerelated with the mobility based on the UE such as cell selection or cellreselection without receiving a command of the network. On the contrary,when the UE is in the ECM-CONNECTED state, the mobility of the UE ismanaged by the command of the network. When a position of the UE in theECM-IDLE state is different from a position which is known to thenetwork, the UE notifies the corresponding position of the UE to thenetwork through a tracking area updating procedure.

Next, the system information will be described.

The system information includes necessary information which the UE needsto known so as to be connected to the BS. Accordingly, the UE needs toreceive all the system information before being connected to the BS, andfurther, needs to have latest system information at all times. Inaddition, since the system information is information to be known by allthe UE in one cell, the BS periodically transmits the systeminformation. System information is divided into a master informationblock (MIB) and a plurality of system information blocks (SIB).

The MIB may include a limited number of parameters required to beobtained for other information from a cell, which are most requisite andare most frequently transmitted. User equipment first finds the MIBafter downlink synchronization. The MIB may include informationincluding a downlink channel bandwidth, a PHICH configuration, an SFNthat supports synchronization and operates as a timing reference, and aneNB transmission antenna configuration. The MIB may bebroadcast-transmitted through a BCH.

System information block type 1 (SIB1) among the included SIBs istransmitted while being included in a message of“SystemInformationBlockType1” and SIBs other than the SIB1 istransmitted while being included in a system information message.Mapping the SIBs to the system information message may be flexiblyconfigured by scheduling information list parameters included in theSIB1. However, each SIB may be included in a single system informationmessage and only SIBs having the same scheduling requirement value(e.g., cycle) may be mapped to the same system information message.Further, system information block type 2 (SIB2) is continuously mappedto a system information message corresponding to a first entry in asystem information message list of a scheduling information list. Aplurality of system information messages may be transmitted within thesame cycle. The SIB1 and all information system information messages aretransmitted through a DL-SCH.

In addition to the broadcast transmission, in the E-UTRAN, the SIB1 maybe dedicatedly signaled while including a parameter similarly to a valueset in the related art and in this case, the SIB1 may be transmittedwhile being included in an RRC connection reconfiguration message.

The SIB1 includes information associated with a user cell access anddefines scheduling of other SIBs. The SIB1 may include PLMN identifiersof the network, a tracking area code (TAC) and a cell ID, a cell barringstatus indicating whether the cell is a cell which may camp on, a lowestreceiving level required in the cell, which is used as a cellreselection reference, and information associated with transmission timeand cycle of other SIBs.

The SIB2 may include radio resource configuration information common toall terminals. The SIB2 may include information associated with anuplink carrier frequency and an uplink channel bandwidth, an RACHconfiguration, a paging configuration, an uplink power controlconfiguration, a sounding reference signal configuration, and a PUCCHconfiguration and a PUSCH configuration supporting ACK/NACKtransmission.

The terminal may apply acquisition and change sensing procedures of thesystem information only to a PCell. In an SCell, the E-UTRAN may provideall system information associated with an RRC connection state operationthrough dedicated signaling when the corresponding SCell is added. Whenthe system information associated with the configured SCell is changed,the E-UTRAN may release and add the considered SCell later and therelease and addition may be performed together with the single RRCconnection reconfiguration message. The E-UTRAN may configure parametervalues other than a value broadcasted in the considered SCell throughthe dedicated signaling.

The terminal needs to guarantee validity of specific type systeminformation and the system information is referred to as required systeminformation. The required system information may be defined as follows.

-   -   In the case where the terminal is in an RRC idle state: It needs        to be guaranteed that the terminal has valid versions of the MIB        and the SIB1 as well as the SIB2 to SIB8 and this may be        followed by supporting a considered RAT.    -   In the case where the terminal is in an RRC connection state: It        needs to be guaranteed that the terminal has the valid versions        of the MIB, the SIB1, and the SIB2.

In general, the validity of the system information may be guaranteedwithin a maximum of 3 hours after the system information is acquired.

Generally, services provided to the UE by the network may be dividedinto three types to be described below. Further, the UE differentlyrecognizes the cell type according to which service may be provided.First, the services types will be described below, and then the celltypes will be described.

1) Limited service: The service provides an emergency call and anearthquake and tsunami warning system (ETWS), and may be provided in anacceptable cell.

2) Normal service: The service means a public use of a general use, andmay be provided in a suitable or normal cell.

3) Operator service: The service means a service for a communicationnetwork operator, and the cell may be used by only the communicationnetwork operator and may not be used by a general user.

In relation to the service type provided by the cell, the cell types maybe divided below.

1) Acceptable cell: A cell in which the UE may receive the limitedservice. The cell is a cell which is not barred and satisfies a cellselection reference of the UE in the corresponding UE.

2) Suitable cell: A cell in which the UE may receive the normal service.The cell satisfies a condition of the acceptable cell and simultaneouslysatisfies additional conditions. As the additional conditions, the cellneeds to belong to a public land mobile network (PLMN) to which thecorresponding UE may be connected and be a cell in which the performanceof the tracking area updating procedure of the UE is not barred. Whenthe corresponding cell is a CSG cell, the UE needs to be a cell to beconnected to the corresponding cell as the CSG member.

3) Barred cell: The cell is a cell which broadcasts information on acell barred through the system information.

4) Reserved cell: The cell is a cell which broadcasts information on acell reserved through the system information.

FIG. 4 is a flowchart illustrating an operation of the UE in the RRCidle state. FIG. 4 illustrates a procedure of registering a UE in whichinitial power is turned on in the network through a cell selectionprocess and reselecting the cell if necessary.

Referring to FIG. 4, the UE selects a radio access technology (RAT) forcommunicating with the PLMN which is a network to receive the service(S410). Information on the PLMN and the RAT may be selected by the userof the UE, and stored in a universal subscriber identity module (USIM)to be used.

The UE selects the measuring BS and a cell having largest value amongcells in which signal intensities and quality measured from the BS arelarger than a predetermined value (Cell Selection) (S420). This isperforming the cell selection by the turned-on UE and may be calledinitial cell selection. The cell selection procedure will be describedbelow. After the cell selection, the UE receives system informationwhich the BS periodically transmits. The aforementioned predeterminedvalue means a value defined in the system for ensuring the quality forthe physical signal in the data transmission/reception. Accordingly, thevalue may vary according to the applied RAT.

The UE performs a network registering procedure in the case wherenetwork registering is required (S430). The UE registersself-information (e.g., IMSI) in order to receive a service (e.g.,paging) from the network. The UE needs not to be registered in theconnected network whenever selecting the cell, but is registered in thenetwork in the case where information (e.g., tracking area identity(TAI)) on the network received from the system information andinformation on a network which is known to the UE.

The UE performs cell reselection based on a service environment, a UEenvironment, or the like which is provide by the cell (S440). The UEselects one of other cells providing a better signal characteristic thanthe cell of the BS to which the UE is connected, when the value of theintensity or the quality of the signal measured from the BS receivingthe service is a value measured from the BS of the neighbor cell. Thisprocess is distinguished from the initial cell selection of the secondprocess to be called cell re-selection. In this case, in order toprevent the cell from being frequently reselected depending on thechange in signal characteristic, there is a temporal constraint. Thecell re-selection procedure will be described below.

FIG. 5 is a flowchart illustrating a process of establishing RRCconnection.

The UE transports an RRC connection request message requesting the RRCconnection to the network (S510). The network transports an RRCconnection setup message in a response for the RRC connection request(S520). After receiving the RRC connection setup message, the UE entersan RRC connection mode.

The UE transports to the network an RRC connection setup completemessage used for verifying successful completion of the RRC connectionestablishment (S530).

FIG. 6 is a flowchart illustrating an RRC connection reconfigurationprocess. The RRC connection reconfiguration is used for modifying theRRC connection. The RRC connection reconfiguration is used for RBestablishment/modify/release, handover performance, and measurementsetup/modify/release.

The network transports to the UE an RRC connection reconfigurationmessage for modifying the RRC connection (S610). The UE transports tothe network an RRC connection reconfiguration complete message used forverifying successful completion of the RRC connection reconfiguration,as a response to the RRC connection reconfiguration (S620).

Hereinafter, the PLMN (Public Land Mobile Network) will be described.

The PLMN is a network which is arranged and operated by a mobile networkoperator. Each mobile network operator operates one or more PLMNs. EachPLMN may be identified as a mobile country code (MCC) and a mobilenetwork code (MNC). PLMN information of the cell is included in thesystem information to be broadcasted.

In PLMN selection, cell selection, and cell re-selection, various typesof PLMNs may be considered by the UE.

Home PLMN (HPLMN): PLMN having a MCC and a MNC matched with the MCC andthe MNC of the UE IMSI.

Equivalent HPLMN (EHPLMN): PLMN handled to be equivalent to the HPLMN.

Registered PLMN (RPLMN): PLMN in which position registration issuccessfully completed.

Equivalent PLMN (EPLMN): PLMN handled to be equivalent to the RPLMN.

Each mobile service consumer is subscribed in the HPLMN. When a generalservice is provided to the UE by the HPLMN or the EHPLMN, the UE is notin a roaming state. On the other hand, when the service is provided tothe UE by a PLMN other than the HPLMN/EHPLMN, the UE is in the roamingstate, and the PLMN is called a visited PLMN (VPLMN).

The UE searches a usable PLMN and selects a suitable PLMN which mayreceive the service when the power is turned on in an initial stage. ThePLMN is a network which is deployed or operated by a mobile networkoperator. Each mobile network operator operates one or more PLMNs. EachPLMN may be identified by a mobile country code (MCC) and a mobilenetwork code (MNC). PLMN information of the cell is included in thesystem information to be broadcasted. The UE attempts to register theselected PLMN. When the registration is completed, the selected PLMNbecomes a registered PLMN (RPLMN). The network may signal a PLMN list tothe UE, and PLMNs included in the PLMN list may be considered as thePLMN such as the RPLMN. The UE registered in the network needs to bereachable by the network at all times. If the UE is in the ECM-CONNECTEDstate (equally, the RRC connection state), the network recognizes thatthe UE receives the service. However, when the UE is in the ECM-IDLEstate (equally, the RRC idle state), the situation of the UE is notvalid in the eNB, but stored in the MME. In this case, the position ofthe UE is in the ECM-IDLE state is notified to only the MME withgranularity of the list of the tracking areas (TAs). A single TA isidentified by a tracking area identity (TAI) constituted by a PLMNidentity to which the TA belongs and a tracking area code (TAC) uniquelyexpressing the TA in the PLMN.

Next, among the cells provided by the selected PLMN, the UE selects acell having signal quality and characteristic which may receive asuitable service.

Next, a procedure of selecting the cell by the UE will be described indetail.

When the power is turned on or the UE stays in the cell, the UE performsprocedures for receiving the service by selecting/re-selecting a cellhaving proper quality.

The UE in the RRC idle state selects the cell having the proper qualityat all times and needs to be prepared to receive the service through theselected cell. For example, the UE in which the power is just turned onneeds to select the cell having the proper quality for registration tothe network. When the UE in the RRC connection state enters the RRC idlestate, the UE needs to select the cell staying in the RRC idle state. Assuch, a process of selecting the cell which satisfies any condition sothat the UE stays in a service stand-by state such as the RRC idle stateis called cell selection. Since the cell selection is performed in astate where the cell in which the UE stays in the RRC idle state is notcurrently determined, it is more important to select the cell as quicklyas possible. Accordingly, so long as the cell is a cell providing radiosignal quality of a predetermined level or more, even though the cell isnot the cell providing the best signal quality to the UE, the cell maybe selected in the cell selection process of the UE.

Hereinafter, with reference to 3GPP TS 36.304 V8.5.0 (2009 March) “UserEquipment (UE) procedures in idle mode (Release 8)”, a method and aprocedure of selecting the cell by the UE in 3GPP LTE will be describedin detail.

The cell selection process is largely divided to two processes.

First, as an initial cell selection process, the UE has no previousinformation on the radio channel in this process. Accordingly, the UEsearches all radio channels in order to find a suitable cell. The UEfinds the strongest cell in each channel. Thereafter, when the UE justfinds the suitable cell stratifying a cell selection reference, the UEselects the corresponding cell.

Next, the UE may select the cell by using the stored information orusing information broadcasted in the cell. Accordingly, the cellselection may be quickly performed as compared with the initial cellselection process. The UE selects the corresponding cell when justfinding the cell satisfying the cell selection reference. If the UE doesnot find the suitable cell satisfying the cell selection referencethrough the process, the UE performs the initial cell selection process.

A cell selection criterion may be defined as shown in Equation 1 givenbelow.Srxlev>0 AND Squal>0  [Equation 1]where:Srxlev=Q _(rxlevmeas)−(Q _(rxlevmin) +Q _(rxlevminoffset))−PcompensationSqual=Q_(qualmeas)−(Q_(qualmin)+Q_(qualminoffset))

Herein, each variable of Equation 1 may be defined as shown in Table 1given below.

TABLE 1 Srxlev Cell selection RX level value (dB) Squal Cell selectionquality value (dB) Q_(rxlevmeas) Measured cell RX level value (RSRP)Q_(qualmeas) Measured cell quality value (RSRQ) Q_(rxlevmin) Minimumrequired RX level in the cell (dBm) Q_(qualmin) Minimum required qualitylevel in the cell (dB) Q_(rxlevminoffset) Offset to the signalledQ_(rxlevmin) taken into account in the Srxlev evaluation as a result ofa periodic search for a higher priority PLMN while camped normally in aVPLMN [5] Q_(qualminoffset) Offset to the signalled Q_(qualmin) takeninto account in the Squal evaluation as a result of a periodic searchfor a higher priority PLMN while camped normally in a VPLMN [5]Pcompensation max(P_(EMAX) − P_(PowerClass), 0) (dB) P_(EMAX) Maximum TXpower level an UE may use when transmitting on the uplink in the cell(dBm) defined as P_(EMAX) in [TS 36.101] P_(PowerClass) Maximum RFoutput power of the UE (dBm) according to the UE power class as definedin [TS 36.101]

Q_(rxlevminoffset) and Q_(qualminoffset) which are signaled values as aresult of a periodic search for a PLMN having a higher priority whilethe terminal camps on a normal cell may be applied only when cellselection is evaluated. During the periodic search for the PLMN havingthe higher priority, the terminal may perform the cell selectionevaluation by using parameter values stored from another cell of thePLMN having the higher priority.

After the UE selects any cell through the cell selection process, theintensity or the quality of the signal between the UE and the BS may bechanged according to mobility of the UE, a change in radio environment,or the like. Accordingly, when the quality of the selected celldeteriorates, the UE may select another cell providing better quality.As such, in the case of selecting the cell again, generally, the UEselects the cell providing better signal quality than the currentlyselected cell. This process is called cell reselection. The cellreselection process generally has a primary object to select a cellproviding the best quality to the UE in terms of the quality of theradio signal.

In addition to the quality of the radio signal, the network determines apriority for each frequency to notify the determined priority to the UE.In the UE receiving the priority, the priority is first considered ascompared the radio signal quality reference in the cell reselectionprocess.

As such, there is the method of selecting or reselecting the cellaccording to a signal characteristic in the radio environment, and inthe case of selecting the cell for reselection during the cellreselection, there may be methods of reselecting the cell according to aRAT of the cell and a frequency characteristic below.

-   -   Intra-frequency cell reselection: The UE reselects a cell having        the same RAT and the same center-frequency as the cell during        camping.    -   Inter-frequency cell reselection: The UE reselects a cell having        the same RAT as and a different center-frequency from the cell        during camping.    -   Inter-RAT cell reselection: The UE reselects a cell using a        different RAT from the RAT during camping.

A principle of the cell reselection process is as follows.

First, the UE measures the quality of the serving cell and the qualityof the neighbor cell for the cell reselection.

Second, the cell reselection is performed based on a cell reselectionreference. The cell reselection reference has the followingcharacteristics in association with the measurement of the serving celland the neighbor cell.

The intra-frequency cell reselection is basically based on ranking. Theranking is an operation of defining index values for evaluating the cellreselection and ranking cells in an order of sizes of the index valuesby using the index values. A cell having the best index value iscommonly called a best ranked cell. The cell index value is based on avalue measured by the UE with respect to the corresponding cell and is avalue applying a frequency offset or a cell offset if necessary.

The inter-frequency cell reselection is based on a frequency priorityprovided by the network. The UE attempts to camp on in a frequencyhaving the highest frequency priority. The network may provide afrequency priority to be commonly applied to the UEs in the cell throughthe broadcast signaling or provide a priority for each frequency forevery UE through dedicated signal for each UE. The cell reselectionpriority provided through the broadcast signaling may be referred to asa common priority, and the cell reselection priority set by the networkfor each UE may be referred to as a dedicated priority. When the UEreceives the dedicated priority, the UE may receive a validity timerelated with the dedicated priority together. When the UE receives thededicated priority, the UE starts a validity timer set as the validitytime received together. The UE applies the dedicated priority in the RRCidle mode while the validity timer operates. When the validity timerends, the UE discards the dedicated priority and applies the commonpriority again.

For the inter-frequency cell reselection, the network may provideparameters (for example, a frequency-specific offset) used in the cellreselection to the UE for each frequency.

For the intra-frequency cell reselection or the inter-frequency cellreselection, the network may provide a neighbor cell list (NCL) used inthe cell reselection to the UE. The NCL includes cell-specificparameters (for example, a cell-specific offset) used in the cellreselection.

For the intra-frequency cell reselection or the inter-frequency cellreselection, the network may provide a cell reselection black list usedin the cell reselection to the UE. The UE does not perform the cellreselection with respect to the cell included in the black list.

Next, the ranking performed in the cell reselection evaluating processwill be described.

A ranking criterion used to give the priority of the cell is defined byEquation 1.R _(S) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) −Q_(offset)  [Equation 1]

Here, R_(s) represents a ranking criterion of the serving cell, R_(n)represents a ranking criterion of the neighbor cell, Q_(meas,s)represents a quality value measured with respect to the serving cell bythe UE, Q_(meas,n) represents a quality value measured with respect tothe neighbor cell by the UE, Q_(hyst) represents a hysteresis value forranking, and Q_(offset) represents an offset between the both cells.

In the intra-frequency, when the UE receives the offset Q_(offsets,n)between the serving cell and the neighbor cell,Q_(offset)=Q_(offsets,n), and when the UE does not receiveQ_(offsets,n), Q_(offset)=0.

In the inter-frequency, when the UE receives the offset Q_(offsets,n)for the corresponding cell, Q_(offset)=Q_(offsets,n)+Q_(frequency), andwhen the UE does not receive Q_(offsets,n), Q_(offset)=Q_(frequency).

When the ranking criterion R_(s) of the serving cell and the rankingcriterion R_(n) of the neighbor cell are changed in a similar state, theranking order is frequently reversed as the changing result, and as aresult, the UE may alternately reselect the two cells. Q_(hyst) is aparameter for preventing the UE from alternately reselecting the twocells by giving the hysteresis in the cell reselection.

The UE measures the R_(s) of the serving cell and the R_(n) of theneighbor cell according to the Equation 1, regards the cell having thelargest ranking criterion value as the best ranked cell, and selects thecell.

According to the reference, it can be seen that the quality of the cellacts as the most important reference in the cell reselection. When thereselected cell is not the suitable cell, the UE excludes thecorresponding frequency or the corresponding cell from the cellreselection target.

When the terminal (UE) perform cell reselection according to the cellreselection evaluation, the terminal may decide that a cell reselectioncriterion is satisfied when the cell reselection criterion is satisfiedfor a specific time and move the cell to the selected target cell.Herein, the specific time may be given from the network as aTreselection parameter. The Treselection may specify a cell reselectiontimer value and be defined with respect to each frequency and anotherRAT of the E-UTRAN.

Hereinafter, cell reselection information used for the cell reselectionby the terminal will be described.

The cell reselection information may be transmitted while being includedin the system information broadcasted from the network in a format ofthe cell reselection parameter and provided to the terminal. The cellreselection parameter provided to the terminal may include the followingtypes.

Cell Reselection Priority: The cellReselectionPriority parameterspecifies the priority of a frequency of the E-UTRAN, a frequency of theUTRAN, a group of GERAN frequencies, a band class of CDMA2000 HRPD, or aband class of CDMA2000 1×RTT.

Qoffset_(s,n): Specifies an offset value between two cells.

Qoffset_(frequency): Specifies a frequency specific offset for theE-UTRAN having the same priority.

Q_(hyst): Specifies a hysteresis value for a rank index.

Q_(qualmin): Specifies a minimally required quality level and specifiedby the unit of dB.

Q_(rxlevmin): Specifies a minimally required Rx level and specified bythe unit of dB.

Treselection_(EUTRA): Specifies the cell reselection timer value for theE-UTRAN and may be configured with respect to each frequency of theE-UTRAN.

Treselection_(UTRAN): Specifies the cell reselection timer value for theUTRAN.

Treselection_(GERA): Specifies the cell reselection timer value for theGERAN.

Treselection_(CDMA) _(_) _(HRPD): Specifies the Cell Reselection TimerValue for the CDMA HRPD.

Treselection_(CDMA) _(_) _(1×RTT): Specifies the cell reselection timervalue for the CDMA 1×RTT.

Thresh_(x, HighP): An Srxlev threshold value used by the terminal whenreselection to an RAT/frequency having a higher priority than a servingfrequency is specified by the unit of dB. Specific threshold values maybe individually configured with respect to the frequencies of theE-UTRAN and the UTRAN, each group of the GERAN frequency, each bandclass, and each band class of the CDMA2000 1×rtt.

Thresh_(x, HighQ): An Squal threshold value used by the terminal whenreselection to the RAT/frequency having the higher priority than theserving frequency is specified by the unit of dB. Specific thresholdvalues may be individually configured with respect to each frequency ofthe E-TRAUN and the UTRAN FDD.

Thresh_(x,LowP): The Srxlev threshold value used by the terminal whenreselection to an RAT/frequency having a lower priority than the servingfrequency is specified by the unit of dB. Specific threshold values maybe individually configured with respect to the frequencies of theE-UTRAN and the UTRAN, each group of the GERAN frequency, each bandclass, and each band class of the CDMA2000 1×rtt.

Thresh_(x, LowQ): The Squal threshold value used by the terminal whenreselection to the RAT/frequency having the lower priority than theserving frequency is specified by the unit of dB. Specific thresholdvalues may be individually configured with respect to each frequency ofthe E-TRAUN and the UTRAN FDD.

Thresh_(Serving, LowP): The Srxlev threshold value used by the terminalon the serving cell when reselection to the lower RAT/frequency isspecified by the unit of dB.

Thresh_(Serving, LowQ): The Squal threshold value used by the terminalon the serving cell when reselection to the lower RAT/frequency isspecified by the unit of dB.

S_(IntraSerachP): An Srxlev threshold value for intra-frequencymeasurement is specified by the unit of dB.

S_(IntraSerachQ): An Squal threshold value for intra-frequencymeasurement is specified by the unit of dB.

S_(nonIntraSerachP): An Srxleve threshold value for E-UTRANintra-frequency and inter-RAT measurement are specified by the unit ofdB.

S_(nonIntraSerachQ): An Squal threshold value for E-UTRANintra-frequency and inter-RAT measurement are specified by the unit ofdB.

Meanwhile, the aforementioned cell reselection parameter may be scaledaccording to mobility of the terminal. The mobility of the terminal maybe estimated based on the number of times when the terminal movesthrough cell reselection and/or handover during a specific time intervaland this is referred to as mobility state estimation (MSE), The mobilityof the terminal may be estimated as one of a normal mobility state, amedium mobility state, and a high mobility state according to the MSE.

A parameter which may be used as a reference for estimating the mobilitystate of the terminal in the MSE may be provided. T_(CRmax) specifies aspecific time interval for counting moving execution of anotherterminal. N_(CR) _(_) _(H) indicates the maximum number of times of cellreselection for entering the high mobility. N_(CR) _(_) _(M) indicatesthe maximum number of times of cell reselection for entering the mediummobility. T_(CRmaxHyst) specifies an additional time interval before theterminal may enter the general mobility state.

A terminal that is in an RRC_IDLE state performs the cell reselectionwhen a cell reselection condition is satisfied. When the number of timesat which the terminal performs the cell reselection for T_(CRmax) ismore than N_(CR) _(_) _(H) which is a first threshold value, a conditionof the high mobility state is satisfied as the mobility state of theterminal. When the number of times at which the terminal performs thecell reselection for T_(CRmax) is more than N_(CR) _(_) _(M) which is asecond threshold value and not more than N_(CR) _(_) _(H) which is thefirst threshold value, a condition of the medium mobility state issatisfied as the mobility state of the terminal. When the number oftimes when the terminal performs the cell reselection for T_(CRmax) isnot more than N_(CR) _(_) _(M) which is the second threshold value, acondition of the normal mobility state is satisfied as the mobilitystate of the terminal. For example, when it is not sensed that theterminal is in the high mobility state and the normal mobility stateduring an additional time interval T_(CRmaxHyst), it may be estimatedthat the terminal is in the normal mobility state. However, when theterminal performs the cell reselection consecutively between two samecells, the cell reselection may not be counted as the number of cellreselection times.

A scaling factor may be specified according to the mobility state of theterminal according to the MSE and the scaling factor may be applied toone or more cell reselection parameters. For example, sf-Medium andsf-High which are scaling factors according to the medium mobility andthe high mobility may be applied to Qhyst, Treselection_(EUTRA),Treselection_(UTRA), Treselection_(GERA), Treselection_(CDMA) _(_)_(HRPD), and Treselection_(CDMA) _(_) _(1×RTT).

Meanwhile, the cell reselection information may be provided to theterminal while being included in an RRC disconnection message which isan RRC message for RRC disconnection between the network and theterminal. For example, the RRC disconnection message may include asubcarrier frequency list and the cell reselection priority of theE-UTRAN, a subcarrier frequency list and the cell reselection priorityof the UTRA-FDD, a subcarrier frequency list and the cell reselectionpriority of the UTRA-TDD, a subcarrier frequency list and the cellreselection priority of the GERAN, the band class list and the cellreselection priority of the CDMA2000 HRPD, and the band class list andthe cell reselection priority of the CDMA2000 1×RTT.

Hereinafter, sharing an RAN by multiple operators will be described.

The multiple operators may provide the service by individuallyconstructing the RAN, but provide the service to a subscriber by sharinga cell constructed by a specific operator. This is referred to as RANsharing. In this case, the cell shared by the multiple providers maybroadcast a PLMN list. The PLMN list may be transmitted while beingincluded in SIB1 of the system information broadcasted by the cell.Meanwhile, a PLMN identifier first listed in the PLMN list included inthe SIB1 may be implemented to indicate a primary PLMN.

Under a situation in which one cell is shared by the multiple operators,the cell reselection information provided by the shared cell may becommonly applied to all PLMNs in the PLMN list. In general, the cellreselection information provided by the shared cell is configured toprimarily coincide with a policy of the primary PLMN. Therefore,terminals receiving a service depending on a secondary PLMN perform thecell reselection based on information other than the cell reselectioninformation optimized for providing the service.

Hereinafter, the handover related with movement of the terminal in theRRC connection state will be described.

FIG. 7 is a flowchart illustrating a handover process.

The terminal (UE) transmits a measurement report to a source basestation (BS) (S710). The source base station decides whether to performthe handover by using the received measurement report. When the sourcebase station decides the handover to a contiguous cell, the continuouscell becomes a target cell and a base station that belongs to the targetcell becomes a target base station (BS).

The source base station transmits a handover preparation message to thetarget base station (S711). The target base station performs admissioncontrol in order to increase a success possibility of the handover.

The target base station transmits a handover preparation acknowledgement(ACK) message to the source base station (S712). The handoverpreparation acknowledgement (ACK) message may include a cell-radionetwork temporary identifier (C-RNTI) and/or a dedicated random accesspreamble. The C-RNTI is an identifier for identifying the terminal inthe cell. The dedicated random access preamble as a preamble which theterminal may exclusively use during a predetermined period is used inperforming the non-contention based random access. The random accessprocess may be divided into a contention based random access processusing the predetermined random access preamble and the non-contentionbased random access process using the dedicated random access preamble.The non-contention based random access process may prevent a delay ofthe handover due to contention with other terminals as compared with thecontention based random access process.

The source base station transmits a handover command message to theterminal (S713). The handover command message may be transmitted in aform of a radio resource control (RRC) connection reconfigurationmessage. The handover command message may include the C-RNTI and thededicated random access preamble received from the target base station.

The terminal receives the handover command message from the source basestation and thereafter, synchronizes with the target base station(S714). The terminal receives a PSS and an SSS of the target basestation to synchronize the PSS and the SS and receives the PBCH toacquire the system information.

The terminal transmits the random access preamble to the target basestation to start the random access process (S715). The terminal may usethe dedicated random access preamble included in the handover commandmessage. Alternatively, if the dedicated random access preamble is notallocated, the terminal may use a predetermined random access preambleselected in a random access preamble set.

The target base station transmits a random access response message tothe terminal (S716). The random access response message may includeuplink resource allocation and/or time offset (timing advance).

The terminal that receives the random access response message adjustsuplink synchronization based on the time offset and transmits a handoverconfirm message to the target base station by using the uplink resourceallocation (S717). The handover confirm message may indicate that thehandover process is completed and be transmitted together with an uplinkbuffer status report.

The target base station transmits a path switch request message to amobility management entity (MME).

The MME transmits a user plane update request message to aserving-gateway (S-GW) (S719).

The S-GW switches a downlink data path to the target base station(S720).

The S-GW transmits a user plane update response message to the MME(S721).

The MME transmits a path switch request ACK message to the target basestation (S722).

The target base station transmits a resource release message to thesource base station to notify the success of the handover (S723).

The source base station release a resource related to the terminal(S724).

Hereinafter, radio link monitoring (RLM) will be described.

The UE monitors downlink quality based on a cell-specific referencesignal in order to detect the downlink radio link quality of the PCell.The UE estimates the downlink radio link quality for monitoring thedownlink radio link quality and compares the estimated quality withthreshold values Qout and Qin. The threshold value Qout is defined as alevel in which the downlink radio link may not be stably received, andcorresponds to a block error rate of 10% of hypothetical PDCCHtransmission by considering a PDFICH error. The threshold value Qin isdefined a downlink radio link quality level which may be more stablyreceived than the level of the Qout and corresponds to a block errorrate of 2% of hypothetical PDCCH transmission by considering a PCFICHerror.

Hereinafter, a radio link failure (RLF) will be described.

The UE continuously performs the measurement in order to maintain thequality of the radio link with the serving cell receiving the service.The UE determines whether the communication is impossible in the currentsituation due to deterioration of the quality of the radio link. Whenthe communication is almost impossible due to the low quality of theserving cell, the UE determines the current situation as a radio linkfailure.

When the radio link failure is determined, the UE gives up thecommunication maintenance with the current serving cell, selects a newcell through the cell selection (or cell reselection) procedure, andattempts the RRC connection re-establishment to the new cell.

In a specification of 3GPP LTE, cases where the normal communication isimpossible are exemplified below:

-   -   a case where the UE determines that there is a serious problem        in the downlink communication link quality based on the radio        quality measuring result of the PHY layer (determines that the        quality of the PCell is low during the RLM.    -   a case where the UE determines that there is a problem in the        uplink transmission when a random access procedure is        continuously failed in a MAC sub-layer.    -   a case where the UE determines that there is a problem in the        uplink transmission when uplink data transmission is        continuously failed in an RLC sub-layer.    -   a case where the UE determines that the handover is failed.    -   a case where a massage received by the UE does not pass through        an integrity check.

Hereinafter, the RRC connection re-establishment procedure will bedescribed in more detail.

FIG. 8 is a diagram illustrating a RRC connection re-establishmentprocedure.

Referring to FIG. 8, the UE stops the used of all radio bearers whichhave been set except for signaling radio bearer #0 (SRB 0) andinitializes each sub-layer of the AS (S810). Further, each sub-layer andthe PHY layer are set as a default configuration. The UE maintains theRRC connection state during such a process.

The UE performs a cell selection procedure for performing the RRCconnection reconfiguration procedure (S820). The cell selectionprocedure in the RRC connection reconfiguration procedure may beperformed the same as the cell selection procedure performed in the RRCidle state of the UE even though the UE maintains the RRC connectionstate.

The UE verifies the system information of the corresponding cell todetermine whether the corresponding cell is a suitable cell or not,after performing the cell selection procedure (S830). When it isdetermined that the selected cell is the suitable E-UTRAN cell, the UEtransmits an RRC connection reestablishment request message to thecorresponding cell (S840).

Meanwhile, when it is determined that the cell selected through the cellselection procedure for performing the RRC connection reestablishmentprocedure is the cell using the RAT other than the E-UTRAN, the UE stopsthe RRC connection reestablishment procedure and enters the RRC idlestate (S850).

The UE may be implemented so that the cell selection procedure and thesuitability verification of the cell by receiving the system informationof the selected cell are finished within a limited time. To this end,the UE may drive a timer according to the starting of the RRC connectionreestablishment procedure. The timer may stop when it is determined thatthe UE selects the suitable cell. When the timer ends, the UE may regardthat the RRC connection reestablishment procedure is failed and enterthe RRC idle state. The timer is hereinafter referred to as a radio linkfailure timer. In LTE specification TS 36.331, a timer called T311 maybe used as the radio link failure timer. The UE may acquire the settingvalue of the timer from the system information of the serving cell.

In the case of receiving and accepting the RRC connectionreestablishment request message from the UE, the cell transmits a RRCconnection reestablishment message to the UE.

The UE receiving the RRC connection reestablishment message from thecell reconfigures the PDCP sub-layer and the RLC sub-layer for the SRB1.Further, the UE calculates various key values related with securitysetting and reconfigures the PDCP sub-layer responsible for the securitywith newly calculated security key values. As a result, the SRB 1between the UE and the cell is opened, and the RRC control message maybe transmitted and received. The UE completes the restarting of theSRB1, and transmits to the cell an RRC connection reestablishmentcomplete message that the RRC connection reestablishment procedure iscompleted (S860).

On the contrary, in the case of receiving and rejecting the RRCconnection reestablishment request message from the UE, the celltransmits a RRC connection reestablishment reject message to the UE.

When the RRC connection reestablishment procedure is successfullyperformed, the cell and the UE perform the RRC connectionreestablishment procedure. As a result, the UE restores a state beforeperforming the RRC connection reestablishment procedure and maximallysecures continuity of the service.

Hereinafter, interworking between the 3GPP based access network andanother access network will be described.

In the 3GPP, access network discovery and selection functions (ANDSF)for discovering and selecting an accessible access network whileintroducing interworking with a non-3GPP access network (e.g., WLAN)from Rel-8 is standardized. The ANDSF may transfer access networkdiscovery information (e.g., WLAN, WiMAX positional information, and thelike) which is accessible at a location of the terminal, inter-systemmobility policies (ISMP) to reflect a policy of a provider, and aninter-system routing policy (ISRP) and the terminal may determine IPtraffic to be transmitted and an access network to be passed throughbased on the information. The ISMP may include a network selection ruleregarding that the terminal selects one active access network connection(for example, WLAN or 3GPP). The ISRP may include a network selectionrule regarding that the terminal selects one or more potential activeaccess network connections (for example, both WLAN or 3GPP). Theinter-system routing policy includes multiple access PDN connectivity(MAPCON), IP flow mobility (IFOM), and non-seamless WLAN offloading.Open mobile alliance device management, or the like is used for dynamicprovision between the ANDSF and the terminal.

The MAPCON is configured by standardizing a technology that configuresand maintains simultaneous multiple PDN connectivity via the 3GPP accessnetwork and the non-3GPP access network and enables seamless trafficoffloading whole active PDN connection unit seamless traffic offloading.To this end, an ANDSF server provides information on an access pointname (APN) that will perform offloading, a priority (routing rule)between the access networks, a time (time of day) to which an offloadingmethod is applied, and information on an access network (validity area)to be offloaded.

The IFOM supports more flexible and subdivided IP flow mobility andseamless offloading than the MAPCON. A technical feature of the IFOMenables the terminal to access the packet data network through differentaccess networks even when being connected to the packet data network byusing the same access point name (APN) and enables the mobility andoffloading units to move to not the packet data network (PDN) but aspecific service IP traffic flow unit to acquire flexibility in serviceproviding. To this end, the ANDSF server provides information on an IPflow that will perform the offloading, the priority (routing rule)between the access networks, the time (time of day) to which theoffloading method is applied, and the information on the access network(validity area) to be offloaded.

Non-seamless WLAN offloading represents a technology that does notchange a path of predetermined specific IP traffic to the WLAN butcompletely offloads traffic so as not to pass through an EPC. Since thisis not anchored to a P-GW for supporting the mobility, the offloaded IPtraffic may not seamlessly to the 3GPP access network again. To thisend, the ANDSF server provides information similar to informationprovided to perform the IFOM to the terminal.

FIG. 9 is a diagram illustrating an example of an environment in whichthe 3GPP access network and the WLAN access network coexist.

Referring to FIG. 9, as the 3GPP access network, cell 1 in which basestation 1 910 is centered and cell 2 in which base station 2 920 iscentered are extended. Further, as the WLAN access network, basicservice set (BSS) 1 in which an access point (AP)1 930 positioned in thecell 1 is centered and BSS2 in which an AP2 940 is centered are extendedand BSS3 in which AP3 950 that exists in cell 2 is centered areextended. Coverage of the cell is illustrated by a solid line andcoverage of the BSS is illustrated by dotted lines.

It is assumed that a terminal 900 is configured to perform communicationthrough the 3GPP access network and the WLAN access network. In thiscase, the terminal 900 may be called a station.

Initially, the terminal 900 establishes connection with the BS1 910 inthe cell 1 to perform traffic processing through the 3GPP accessnetwork.

The terminal 900 may enter coverage of the BSS1 while moving in coverageof cell 1 and discover the BSS1 through scanning. In this case, theterminal 900 may be connected with the WLAN access network by performingassociation and authentication procedures with the AP1 930 of the BSS1.As a result, the terminal 900 may process the traffic through the 3GPPaccess network and the WLAN access network. Meanwhile, when the terminal900 moves to deviate from the coverage of the BSS1, connection with theWLAN access network may end.

The terminal 900 continuously moves in the coverage of the cell 1 tomove to the vicinity of a boundary between the cell 1 and the cell 2 andenters the coverage of the BSS2 to discover the BSS2 through scanning.In this case, the terminal 900 may be connected with the WLAN accessnetwork by performing the association and authentication procedures withthe AP2 940 of the BSS2. Meanwhile, since the terminal 900 in thecoverage of the BSS2 is positioned on the boundary of the cell 1 and thecell 2, service quality through the 3GPP access network may not beexcellent. In this case, the terminal 900 may operate to concentrativelyprocess the traffic through the WLAN access network.

When the terminal 900 moves to deviate from the coverage of the BSS2 andenters the center of the cell 2, the terminal 900 may terminate theconnection with the WLAN access network and process the traffic throughthe 3GPP access network based on the cell 2.

The terminal 900 may enter the coverage of the BSS3 while moving in thecoverage of cell 2 and discover the BSS1 through scanning. In this case,the terminal 900 may be connected with the WLAN access network byperforming the association and authentication procedures with the AP3950 of the BSS3. As a result, the terminal 900 may process the trafficthrough the 3GPP access network and the WLAN access network.

As described in the example of FIG. 9, under a wireless communicationenvironment in which the 3GPP access network and the non-3GPP accessnetwork coexist, the terminal may adaptively process the traffic throughthe 3GPP access network and/or the non-3GPP access network.

One of primary objects of performing interworking is to control the loadof the access network by offloading the traffic. To this end, the basestation may move some terminals among terminals which establish the RRCconnection to another access network according to a load level of theCN. Therefore, the base station may decide a load control level of thenetwork and easily control the load.

Meanwhile, in the interworking between the 3GPP access network and thenon-3GPP access network in the related art, the terminal selects aspecific access network according to the ANDSF policy and processes thetraffic through the selected access network. In this case, the basestation may not control the interworking between the 3GPP access networkand the non-3GPP access network. Therefore, the radio resource is notnormally allocated to terminals that receive the service in the cell tocause a problem in that the quality of service (QoS) of the terminalsdeteriorates.

A traffic routing criterion needs to be provided to the terminal inorder for the terminal to process the traffic through the non-3GPPaccess network suitable for traffic routing. Further, the base stationneeds to acquire information on the non-3GPP access network around theterminal and determine whether the traffic processing through thenon-3GPP access network is appropriate in order to control theinterworking between the access networks.

By such a point, the present invention proposes a method in which theterminal receives the traffic routing criterion from the base stationand performs traffic routing evaluation for traffic routing to thenon-3GPP access network. Further, in the embodiment of the presentinvention, the traffic routing evaluation may be used to route thetraffic to the non-3GPP access network to the 3GPP access network. Inaddition, proposed is a communication method in which the terminalprovides information on a result of the traffic routing evaluation tothe base station to allow the 3GPP access network and/or the non-3GPPaccess network such as the base station and the AP to control theprocessing the 3GPP traffic/non-3GPP traffic through the trafficrouting.

Hereinafter, in describing the communication method that providessetting the traffic routing criterion, it will be described that thenon-3GPP access network is the WLAN access network as an example.However, the scope of the present invention is not limited thereto andmay be applied even to communication of the terminal associated withother access networks.

FIG. 10 is a diagram illustrating an example of a communication methodaccording to an embodiment of the present invention.

Referring to FIG. 10, the terminal receives a traffic routingconfiguration (S1010). The traffic routing information may betransmitted from the 3GPP access network.

The traffic routing configuration may be provided to the terminalthrough the broadcast signaling from the 3GPP access network. Forexample, the traffic routing configuration may be transmitted whilebeing included in the system information broadcasted by the 3GPP accessnetwork.

The traffic routing configuration may be provided to the terminalthrough the dedicated signaling from the 3GPP access network. Forexample, the traffic routing configuration may be transmitted whilebeing included in the RRC message.

The traffic routing configuration may specify the traffic routingcriterion. The traffic routing criterion may define one or more routingevents and parameters associated with the routing events. The terminalmay perform the traffic routing evaluation based on the routingcriterion and decide whether to report the evaluation result.

The traffic routing configuration may include a concerned WLAN list. Theconcerned WLAN list may include one or more concerned WLANs. Herein, theconcerned WLAN may mean a WLAN access network entity in which the 3GPPtraffic processing is considered to be potentially permitted. Theconcerned WLAN list may be constituted by one or more concerned WLANidentifiers and the identifiers which may be included in the concernedWLAN list will be described below.

1) WLAN SSID (Service Set Identifier): The WLAN SSID may beduplicatively used in a plurality of BSSs.

2) WLAN BSSID (Basic Service Set Identifier): The WLAN BSSID asinformation for identifying a BSS managed by a specific AP may begenerally set as an MAC address of the corresponding AP.

3) HESSID (Homogeneous Extended Service Set Identifier): The HESSID asthe same value as one BSSID among APs and an identifier set by a hotspotoperator may be set in the form of the MAC address. All APs in a hotspotnetwork may be set the same HESSID value.

4) Domain name list: The domain name list may include one or more domainnames of the WLAN access network entity.

The traffic routing configuration may include priority informationregarding the concerned WLAN included in the concerned WLAN list. Thepriority information may indicate a priority with which the terminalpreferentially performs the traffic routing evaluation and accesses withrespect to one or more concerned WLANs included in the concerned WLANlist. That is, the terminal may attempt the traffic routing evaluationfor a concerned WLAN having a highest priority among the discoveredWLANs. The priority information may be implemented not as separateinformation but as the order of identifiers arranged in the concernedWLAN list. A concerned WLAN at an identifier arranged earlier may have ahigher priority or otherwise.

The traffic routing configuration may include one or more routingevents. Each routing event may specify a detailed condition for thetraffic routing evaluation. The traffic routing event may be implementedas follows. The traffic routing criterion may be configured by one ormore combinations of routing events described below.

1) The discovered WLAN access network entity is included in theconcerned WLAN list of the traffic routing configuration.

2) The signal quality of the discovered WLAN access network entity ishigher than a specific quality threshold value.

3) The load level of the discovered WLAN access network is lower than aspecific load threshold value.

4) The speed of the backhaul link associated with the discovered WLANaccess network is higher than a specific speed threshold value. Thebackhaul link may be a distribution system (DS). The speed of thebackhaul link may be an uplink traffic processing speed of the DS and/ora downlink traffic processing speed of the DS.

The traffic routing configuration may include additional informationwhich may be used to evaluate whether the traffic routing criteriondepending on the routing event is satisfied. For example, the trafficrouting configuration may include at least one of the quality thresholdvalue, the load threshold value, and the speed threshold value.

In the traffic routing criterion specified by the traffic routingconfiguration, the routing event for the concerned WLAN list may beparticularly be implemented to be included in the traffic routingcriterion.

When the WLAN signal transmitting and receiving functions are notactivated, the terminal that receives the traffic routing configurationmay operate to enable WLAN communication by activating the correspondingfunctions.

The terminal that receives the traffic routing configuration mayperforms searching the WLAN access network (S1020). Searching the WLANaccess network may be an operation in which the terminal discoverscontiguous WLAN access network entities by performing the scanning. Thescanning performed by the terminal may be performed according to passivescanning and/or active scanning defined in the WLAN.

According to the passive scanning, the terminal may discover the WLANaccess network entity through receiving a beacon frame transmitted fromthe WLAN access network entity. The terminal may discover an AP and/or anon-AP station that transmits the beacon frame. All or some of the WLANsystem information are included in the probe response frame transmittedfrom the AP and/or the non-AP station. In more detail, as theidentification information for the WLAN access network entity for thecorresponding AP and/or the non-AP station, the BSSID, the SSID, theHESSID, and the like may be included in the beacon frame. Further, thecapability information which may be supported by the WLAN access networkentity may be included in the beacon frame.

According to the active scanning, the terminal may transmit a proberequest frame. The probe request frame may be transmitted in a broadcastscheme. The terminal may receive a probe response frame from a specificWLAN access network entity as a response to the probe request frame anddiscover the corresponding WLAN access network entity. The terminal maydiscover an AP and/or a non-AP station that transmits the probe responseframe. All or some of the WLAN system information are included in theprobe response frame transmitted from the AP and/or the non-AP station.In more detail, as identification information for the WLAN accessnetwork entity for the corresponding AP and/or the non-AP station, theBSSID, the SSID, the HESSID, and the like may be included in the proberesponse frame. Further, capability information which may be supportedby the WLAN access network entity may be included in the probe responseframe.

The terminal performs the traffic routing criterion evaluation for thediscovered WLAN access network entity (S1030). The terminal may performthe evaluation based on the traffic routing criterion configured in theterminal through the traffic routing configuration. In more detail, theterminal may determine whether one or more routing events providedthrough the traffic routing configuration for the traffic routingcriterion evaluation is satisfied.

When the traffic routing criterion is specified by a plurality ofrouting events, the terminal may decide that the traffic routingcriterion is satisfied when one of the plurality of routing events issatisfied. Alternatively, when the traffic routing criterion isspecified by the plurality of routing events, the terminal may decidethat the traffic routing criterion is satisfied when all of theplurality of routing events are satisfied.

For example, as described above, the traffic routing configuration maybe implemented so that the routing event for the concerned WLAN list isrequisitely included in the traffic routing criterion. In this case, theterminal may preferentially determine whether the discovered WLAN accessnetwork is included in the concerned WLAN list. As a result of thedetermination, the terminal may determine whether the traffic routingcriterion is satisfied according to residual routing vents for the WLANaccess network that is confirmed that the WLAN network is included inthe WLAN list. When configured conditions according to all routingevents are satisfied, the terminal may decide that the correspondingWLAN access network satisfies the traffic routing criterion.

The terminal reports a traffic routing criterion evaluation result(S1040). The evaluation result may be reported to the 3GPP accessnetwork through a specific RRC message. The RRC message may be aterminal information reporting message.

The evaluation result may include at least one of information describedbelow.

1) Identifiers of one or more WLAN access network entities that satisfythe traffic routing criterion

2) WLAN channel information of one or more WLAN access network entitiesthat satisfy the traffic routing criterion Herein, the channelcorresponds to a physical medium having a specific frequency band and aspecific bandwidth unlike a channel discussed in the 3GPP access networkand hereinafter, the channel will be referred to as a WLAN channel fordistinguishing from the channel in the 3GPP access network.

3) Presence of traffic to be routed and processed to the WLAN accessnetwork

4) Information on the traffic which may be routed and processed to theWLAN access network. Meanwhile, a type of the traffic which may beprocessed through routing may be as follows.

-   -   Best effort traffic (e.g., non-delay traffic such as Internet        traffic other than a real-time game requiring VoIP or a        stringent delay budget)    -   Traffic which is serviced on a specific CQI depending on a        network configuration such as signaling of a QoS class        identifier (QCI) list or predetermined QCI values    -   Traffic that belongs to a specific APN by a network        configuration OR such as a predetermined APN    -   Information on the traffic type may be implemented as a list        including a radio bearer identifier associated with the        corresponding traffic.

After the traffic routing criterion evaluation for all of the discoveredWLAN access network ends, the terminal may report the evaluation resultto the 3GPP access network. In this case, information on one or moreWLAN access network entities may be included in the evaluation result.For example, when the plurality of WLAN access network entities satisfythe traffic routing criterion, a plurality of WLAN access networkentities may be included in the evaluation result.

Alternatively, when the discovered specific WLAN access network entitysatisfies the traffic routing criterion, the terminal may report anevaluation result associated with the corresponding entity to the 3GPPaccess network. In this case, information on the corresponding WLANaccess network entity may be included in the evaluation result. Anentity which is discovered but not yet subjected to the traffic routingcriterion may be evaluated when traffic routing to the WLAN accessnetwork entity that triggers the evaluation result reporting is notinstructed.

The 3GPP access network that receives the evaluation result may decidewhether the traffic routing instruction is routed to the terminal. The3GPP access network may decide whether the WLAN access network entity isappropriate to the traffic routing and/or whether the traffic type isappropriate to the routing based on the information included in theevaluation result. Further, when the 3GPP access network receives areport of the evaluation result including the plurality of WLAN accessnetwork entities, the 3GPP access network may select a specific entityfor the traffic routing and notify the selected specific entity to theterminal through the traffic routing instruction. As a result, the 3GPPaccess network may transmit the traffic routing instruction to theterminal. The traffic routing instruction may include the followinginformation.

1) Target WLAN information (e.g., the WLAN identifier lists (includingBSSID, SSID, HESSID, and the like) indicating the network entity forwhich the terminal will process the traffic by routing the 3GPP traffic.When no WLAN identifier is included in the target WLAN information, thetraffic processing through the WLAN access network entity receivedthrough the reporting result is not permitted.

2) Traffic information indicating traffic which is permitted to berouted to a routing target entity Similarly, the traffic information mayindicate which traffic routing is required and in this case, theindication of the traffic may be performed through the radio beareridentifier. The traffic information may be configured to instruct toroute and process all traffic to the WLAN access network. When thetraffic information includes no radio bearer identifier, that is, whenthe traffic information indicates no traffic, it may be indicated thatthe traffic routing is not permitted.

3) Information instruct to release the RRC connection after all trafficis routed and processed

4) Information on a WLAN in which the traffic routing is permittedand/or not permitted.

5) Information on a traffic routing direction indicating whether thetraffic routing is performed to the WLAN entity from the 3GPP accessnetwork and/or whether the traffic routing is performed to the 3GPPaccess network from the WLAN entity

The 3GPP access network transmits the traffic routing indicationincluding the information and receives the traffic routing indication(S1050). When the traffic routing indication indicates that the routingis not permitted or when the terminal may not receive the trafficrouting indication within a specific time, the terminal may startdiscovering a new WLAN access network entity or perform the trafficrouting criterion evaluation for the residual discovered WLAN accessnetwork entities.

The terminal that receives the traffic routing indication processes thetraffic through the WLAN access network based on the traffic routingindication (S1060).

The terminal may access the WLAN access network entity indicated by thetraffic routing indication. The terminal's access to the concerned WLANaccess network entity may include performing the association andauthentication procedures with the corresponding AP. The associationprocedure may be performed as the terminal transmits the associationrequest frame to the WLAN access network entity and receives theassociation response frame from the AP as a response thereto. Theauthentication procedure may be performed through transmission/receptionof an authentication frame between the terminal and the WLAN accessnetwork entity.

The terminal processes the traffic indicated to be processed by thetraffic routing indication through the WLAN access network. When thetraffic routing indication indicates that all traffic is routed andprocessed, the terminal may route and process traffic for allestablished radio bearers to the accessed WLAN access network.

Meanwhile, when traffic routing direction information indicating thatthe WLAN traffic is processed through the 3GPP access network by thetraffic routing indication is included, the terminal may process theWLAN traffic through the 3GPP access network. When the RRC connection isnot established through the 3GPP access network, the terminal mayperform an RRC connection establishment and reestablishment procedure.Meanwhile, when the terminal starts processing the WLAN traffic throughthe 3GPP access network or the processing is completed, the terminal maycancel association with the WLAN.

The terminal may report a traffic routing result to the 3GPP accessnetwork. The traffic routing result may indicate whether the terminalsuccess in attempting the traffic routing.

When the terminal accesses the WLAN access network and processes allindicated traffic, the terminal may transmit a traffic routing resultmessage indicating that the traffic routing is successful to the 3GPPaccess network.

When the terminal accesses the WLAN access network, but may not processall indicated traffic, the terminal may transmit the traffic routingresult message indicating that the traffic routing is unsuccessful tothe 3GPP access network. In more detail, the traffic routing resultmessage may be configured to indicate that the authentication andassociation for the WLAN access network is successful, but the trafficprocessing is unsuccessful.

When the terminal fails to access the WLAN access network not to processthe traffic, the terminal may transmit the traffic routing resultmessage indicating that accessing the WLAN access network isunsuccessful to the 3GPP access network. In more detail, the trafficrouting result message may be configured to indicate the authenticationor association.

When the 3GPP access network receives the traffic routing resultindicating that the traffic routing is successfully completed from theterminal, the 3GPP access network may transfer information indicting thetraffic routing result to an MME (alternatively, equivalent core networknode). The corresponding information may include at least one of thetraffic routing result associated with a change of a radio bearerconfiguration, and the like and the information indicating the trafficrouting target WLAN access network entity.

The MME (alternatively, equivalent core network node) received from the3GPP access network may request re-route a data flow toward thecorresponding 3GPP access network to the traffic routing target WLANaccess network entity to the S-GW. The re-routing may be performed by aroute switching procedure.

The success or failure of the re-routing may be notified to the MME andnotified to the 3GPP access network again. As a result, the 3GPP accessnetwork may notify the success or not of the traffic routing procedureto the terminal and this may be implemented by transmitting a trafficrouting confirmation message to the terminal.

There is no remaining radio bearer by processing all traffic and theterminal that successfully reports the traffic routing result mayrelease the RRC connection. The RRC connection release may be performedsubsequently to reporting the traffic routing result. Alternatively, thetraffic routing confirmation message by the 3GPP access network isreceived as a response to the traffic routing result reporting and thetraffic routing confirmation message may be received after confirmingthat the traffic routing is successfully performed.

The terminal that fails to processing the traffic may process thetraffic through the 3GPP access network based on the RRC configurationreceived before the traffic routing indication. The terminal thatalready releases the RRC connection may start the RRC connectionreestablishment procedure.

FIG. 11 is a diagram illustrating one example of a communication methodaccording to an embodiment of the present invention.

Referring to FIG. 11, it is assumed that the terminal supports bothcommunication based on LTE and communication based on the WLAN and it isassumed that the LTE communication and the WLAN communication may beindependently performed. It is assumed that the terminal receives theservice by establishing connection with cell 1. It is assumed that theBSS1 is extended in the coverage of the cell 1.

The terminal receives the traffic routing configuration from the cell 1(S1110). The traffic routing configuration specifies the traffic routingcriterion for the traffic routing of the terminal. The traffic routingconfiguration may include a concerned WLAN list and routing eventsassociated with a WLAN load. The concerned WLAN list may include BSSID1.

The terminal performs scanning for searching the concerned WLAN (S1120).The terminal may perform the passive scanning. Through the passivescanning, the terminal receives the beacon frame transmitted from the APof the BSS1 to discover the BSS1. The BSSID of the BSS1 and the systeminformation for operating the WLAN in the BSS1 may be included in thebeacon frame. The load information of the BSS1 may be included in thesystem information of the beacon frame and the load information mayindicate L₁ as a load level of the BSS1.

The terminal performs the traffic routing criterion evaluation for theBSS1 (S1130). The terminal may perform the traffic routing criterionevaluation by considering whether the BSS1 corresponds to the concernedWLAN depending on the concerned WLAN list and whether the load level ofthe BSS1 is lower than a specific load threshold value L_(TH).

The terminal may find that the BSSID1 which is the identifier of theBSS1 discovered through the scanning is included in the concerned WLANlist. Further, it may be found that the load level L1 of the BSS1 islower than the load threshold value L_(TH) through the load informationof the BSS1 acquired through the scanning. Therefore, the terminal maydecide that the BSS1 satisfies the traffic routing criterion.

The terminal reports a traffic routing criterion evaluation result tothe cell 1 (S1140). The evaluation result may include the identifier ofthe BSS1. Additionally, the evaluation result may further include thepresence of traffic which is permitted to be routed and processed,traffic information associated with the traffic type, and WLAN channelinformation of the BSS1.

The cell 1 that receives the evaluation result decides whether thetraffic routing indication is transmitted and transmits the trafficrouting indication to the terminal (S1150). The traffic routingindication may include the identifier of the BSS1 which is the targetWLAN access network entity for which the 3GPP traffic is to beprocessed. Additionally, the traffic routing indication may includeinformation for identifying traffic to be routed and processed to theBSS1. The traffic information may include a radio bearer identifierlist. Further, the traffic routing indication may further includeinformation for instructing to release the RRC connection aftersuccessful processing of the traffic.

The terminal that receives the traffic routing indication performs theassociation/authentication procedure to perform the WLAN communicationin the BSS1 (S1160). The terminal transmits and receives theauthentication frame to and from the AP of the BSS1 and exchanges theassociation request frame and the association response frame to performthe authentication and association procedures.

The terminal processes the traffic through the AP of the BSS1 (S1170).The terminal may process the 3GPP traffic through the BSS1 as indicatedby the traffic routing indication. The terminal may process the trafficindicated by the traffic routing indication through the BSS1 and processresidual traffic through the cell 1. Meanwhile, when information on thetraffic to be routed and processed by the traffic routing indication isnot provided to the terminal, the terminal may process all trafficthrough the BSS1 or adaptively process some or all of the trafficthrough the BSS1 according to a service environment in the cell 1 andthe BSS1.

The terminal that completes the traffic processing through the BSS1reports the traffic routing result to the cell 1 (S1180). The trafficrouting result may indicate that the traffic indicated by the trafficrouting indication and/or all traffic is successfully processed.

The terminal reports the traffic routing result to the cell 1 andthereafter, performs an RRC connection release procedure with the cell 1(S1190).

Meanwhile, if possible, the terminal may process the traffic through thecell 1 while processing the traffic through the AP of the BSS1. In thiscase, what degree of traffic among all traffic to process through theWLAN access network may be adaptively decided according to the serviceenvironment in the cell 1 and the BSS1.

FIG. 12 is a diagram illustrating another example of the communicationmethod according to the embodiment of the present invention.

Referring to FIG. 12, it is assumed that the terminal supports both thecommunication based on the LTE and the communication based on the WLANand it is assumed that the LTE communication and the WLAN communicationmay be independently performed. It is assumed that the terminal receivesthe service by establishing connection with cell 1. It is assumed thatthe BSS1 and the BSS2 are extended in coverage of the cell 1.

The terminal receives the traffic routing configuration from the cell 1(S1210). The traffic routing configuration specifies the traffic routingcriterion for the traffic routing of the terminal. The traffic routingconfiguration may include a concerned WLAN list and routing eventsassociated with a WLAN load. The concerned WLAN list may include theBSSID2 and the BSSID1. The terminal may find that the BSS2 has a higherpriority than BSS2 according to an arrangement order of the BSSID.

The terminal performs scanning for searching the concerned WLAN (S1220).The terminal may perform the passive scanning.

Through the passive scanning, the terminal receives the beacon frametransmitted from the AP of the BSS1 to discover the BSS1 (S1221). TheBSSID of the BSS1 and the system information for operating the WLAN inthe BSS1 may be included in the beacon frame. The load information ofthe BSS1 may be included in the system information of the beacon frameand the load information may indicate L₁ as the load level of the BSS1.

Through the passive scanning, the terminal receives the beacon frametransmitted from the AP of the BSS2 to discover the BSS2 (S1222). TheBSSID of the BSS2 and the system information for operating the WLAN inthe BSS2 may be included in the beacon frame. The load information ofthe BSS2 may be included in the system information of the beacon frameand the load information may indicate L₂ as the load level of the BSS2.

The terminal performs the traffic routing criterion evaluation for theBSS2 (S1231). Since the terminal may find that the priority for the BSS2is high through the concerned WLAN list of the traffic routingconfiguration, the terminal may preferentially perform the trafficrouting criterion evaluation for the BSS2. The terminal may perform thetraffic routing criterion evaluation by considering whether the BSS2corresponds to the concerned WLAN depending on the concerned WLAN listand whether the load level of the BSS2 is lower than a specific loadthreshold value L_(TH).

The terminal may find that the BSSID2 which is the identifier of theBSS2 discovered through the scanning is included in the concerned WLANlist. Further, it may be found that the load level L₂ of the BSS2 islower than the load threshold value L_(TH) through the load informationof the BSS2 acquired through the scanning. Therefore, the terminal maydecide that the BSS2 satisfies the traffic routing criterion.

The terminal may be configured not to report the evaluation resultimmediately even though a specific BSS satisfies the traffic routingcriterion and to perform the traffic routing criterion evaluation evenwith respect to residual BSSs. As a result, the terminal performs thetraffic routing criterion evaluation for the BSS1 subsequently to theevaluation of the BSS2 (S1232). The terminal may perform the trafficrouting criterion evaluation by considering whether the BSS1 correspondsto the concerned WLAN depending on the concerned WLAN list and whetherthe load level of the BSS1 is lower than a specific load threshold valueL_(TH).

The terminal may find that the BSSID1 which is the identifier of theBSS1 discovered through the scanning is included in the concerned WLANlist. Further, it may be found that the load level L1 of the BSS1 islower than the load threshold value L_(TH) through the load informationof the BSS1 acquired through the scanning. Therefore, the terminaldecides that the BSS2 satisfies the traffic routing criterion.

The terminal reports a traffic routing criterion evaluation result tothe cell 1 (S1240). The evaluation result may include an evaluationresult for the BSS1 and an evaluation result for the BSS2.

The evaluation result may include the identifiers of the BSS1 and theBSS2. Additionally, the evaluation result may further include thepresence of traffic which is permitted to be routed and processed,traffic information associated with the traffic type, and WLAN channelinformation of the BSS1 and BSS2.

The cell 1 that receives the evaluation result decides whether thetraffic routing indication is transmitted and transmits the trafficrouting indication to the terminal (S1250). The traffic routingindication may include the identifier of the BSS2 which is the targetWLAN access network entity for which the 3GPP traffic is be processed.Additionally, the traffic routing indication may include information foridentifying traffic to be routed and processed to the BSS2. The trafficinformation may include the radio bearer identifier list.

The terminal that receives the traffic routing indication performs theassociation/authentication procedure to perform the WLAN communicationin the BSS2 (S1260). The terminal transmits and receives theauthentication frame to and from the AP of the BSS2 and exchanges theassociation request frame and the association response frame to performthe authentication and association procedures.

The terminal processes the traffic through the AP of the BSS2 (S1270).The terminal may process the 3GPP traffic through the BSS2 as indicatedby the traffic routing indication. The terminal may process the trafficindicated by the traffic routing indication through the BSS2 and processresidual traffic through the cell 1. Meanwhile, when information on thetraffic to be routed and processed by the traffic routing indication isnot provided to the terminal, the terminal may process all trafficthrough the BSS2 or adaptively process some or all of the trafficthrough the BSS2 according to a service environment in the cell 1 andthe BSS2.

The terminal that completes the traffic processing through the BSS2reports the traffic routing result to the cell 1 (S1281). The trafficrouting result may indicate that the traffic indicated by the trafficrouting indication and/or all traffic is successfully processed.

The cell 1 confirms whether the traffic routing is successfullyperformed based on the traffic routing result. The cell 1 deciding thatthe traffic routing is successfully performed transmits traffic routingconfirmation to the terminal (S1282).

The terminal that receives the traffic routing confirmation performs theRRC connection release procedure with the cell 1 (S1290).

FIG. 13 is a diagram illustrating yet another example of thecommunication method according to the embodiment of the presentinvention.

Referring to FIG. 13, it is assumed that the terminal supports bothcommunication based on LTE and communication based on the WLAN and it isassumed that the LTE communication and the WLAN communication may beindependently performed. It is assumed that the terminal receives theservice by establishing connection with cell 1. It is assumed that theBSS1 and the BSS2 are extended in coverage of the cell 1.

The terminal receives the traffic routing configuration from the cell 1(S1310). The traffic routing configuration specifies the traffic routingcriterion for the traffic routing of the terminal. The traffic routingconfiguration may include the concerned WLAN list. The concerned WLANlist may include the BSSID2 and the BSSID1. The terminal may find thatthe BSS2 has a higher priority than BSS1 according to an arrangementorder of the BSSID in the concerned WLAN list.

The terminal performs scanning for searching the concerned WLAN (S1320).The terminal may perform the passive scanning.

Through the passive scanning, the terminal receives the beacon frametransmitted from the AP of the BSS1 to discover the BSS1 (S1321). TheBSSID of the BSS1 and the system information for operating the WLAN inthe BSS1 may be included in the beacon frame.

Further, the terminal receives the beacon frame transmitted from the APof the BSS2 to discover the BSS2 (S1322). The BSSID of the BSS2 and thesystem information for operating the WLAN in the BSS2 may be included inthe beacon frame.

The terminal performs the traffic routing criterion evaluation for theBSS2 (S1330). Since the terminal may find that the priority for the BSS2is high through the concerned WLAN list of the traffic routingconfiguration, the terminal may preferentially perform the trafficrouting criterion evaluation for the BSS2. The terminal may perform thetraffic routing criterion evaluation by considering whether the BSS2corresponds to the concerned WLAN depending on the concerned WLAN list.In this example, since the identifier of the BSS2 discovered through thescanning is included in the concerned WLAN list, the terminal may decidethat the BSS2 satisfies the traffic routing criterion.

The terminal may be configured to immediately report the evaluationresult even though a specific BSS satisfies the traffic routingcriterion evaluation. Therefore, the terminal does not perform thetraffic routing criterion evaluation for the BSS1 and reports thetraffic routing criterion evaluation result to the cell 1 (S1340). Theevaluation result may include the identifier of the BSS2. Additionally,the evaluation result may further include the presence of traffic whichis permitted to be routed and processed, traffic information associatedwith the traffic type, and WLAN channel information of the BSS2.

The cell 1 that receives the evaluation result decides whether thetraffic routing indication is transmitted and transmits the trafficrouting indication to the terminal (S1350). The traffic routingindication may include the identifier of the BSS2 which is the targetWLAN access network entity for which the 3GPP traffic is to beprocessed. Additionally, the traffic routing indication may includeinformation for identifying traffic to be routed and processed to theBSS2. The traffic information may include the radio bearer identifierlist. Further, the traffic routing indication may further includeinformation for instructing to release the RRC connection aftersuccessful processing of the traffic.

The terminal that receives the traffic routing indication performs theassociation/authentication procedure to perform the WLAN communicationin the BSS2 (S1360). The terminal transmits and receives theauthentication frame to and from the AP of the BSS1 and exchanges theassociation request frame and the association response frame to performthe authentication and association procedures.

Meanwhile, the terminal may fail to the authentication/association withthe BSS2. As a result, the terminal reports the traffic routing resultto the cell 1 (S1370). The traffic routing result may specify that thetraffic routing is unsuccessful. In more detail, the traffic routingresult may be configured to indicate that the authentication orassociation with the BSS2 is unsuccessful.

The terminal that fails to accessing the WLAN access network performsthe traffic processing through the cell 1 (S1380).

Additionally, the terminal may start the traffic routing criterionevaluation for the BSS1. When the BSS1 satisfies the traffic routingcriterion evaluation, the terminal may report the evaluation resultagain and receive the traffic routing indication indicating that thetraffic is routed to the BSS1. Therefore, the terminal may attempt thetraffic processing through the BSS1.

Additionally, the traffic routing indication may include traffic routingdirection information representing whether the routing to the WLANaccess network from the 3GPP access network is to performed or whetherthe traffic routing to the 3GPP access network from the WLAN accessnetwork is to be performed. The terminal that receives the trafficrouting indication including the traffic routing direction informationperforms the traffic routing in a direction indicated by the trafficrouting direction. The terminal follows the aforementioned routingprocedure when the routing from the 3GPP access network to the WLANaccess network is indicated. When the routing from the WLAN accessnetwork to the 3GPP access network is indicated, the terminal performsthe traffic processing of some or all of the traffic which is processedin the WLAN access network. When there is no RRC connection, theterminal makes the RRC connection with the 3GPP access network andthereafter, processes the traffic in the WLAN access network in the 3GPPaccess network. After the terminal makes the successful RRC connectionin the 3GPP access network or data processing starts in the 3GPP accessnetwork, the terminal may release the connection with the WLAN accessnetwork.

The terminal and the base station performs setting/evaluating thetraffic routing criterion, evaluation result reporting, and trafficprocessing through the WLAN in the aforementioned embodiment, but thepresent invention is not limited thereto. That is, the traffic routingcriterion for the general non-3GPP access network may be set/evaluatedand the terminal may generate the information on the non-3GPP accessnetwork and report the generated information to the network. Further,the terminal may process some or all of the 3GPP traffic through thenon-3GPP access network.

According to the communication method of the embodiment of the presentinvention, in the interworking between the 3GPP access network and thenon-3GPP access network, the base station of the 3GPP access network maycontrol the interworking. The base station controls the operation of theterminal with a control right for the terminal to control the loads ofthe core network and the radio link. Therefore, the base station cansatisfy the terminal that receives the service in the cell or the QoS ofthe specific traffic of the terminal by efficiently using the radioresource.

FIG. 14 is a block diagram illustrating a wireless apparatus in which anembodiment of the present invention can be implemented. The apparatusmay implement the terminal and/or network (base station or anothernetwork entity) in the embodiment of FIGS. 10 to 13.

Referring to FIG. 14, the wireless apparatus 1400 includes a processor1410, a memory 1420, and a radio frequency (RF) unit 1430.

The processor 1410 implements a function, a process, and/or a methodwhich are proposed. The processor 1410 may be configured to set thetraffic routing criterion and/or evaluate whether the traffic routingcriterion is satisfied in order to process the 3GPP traffic through thenon-3GPP access network according to the embodiment of the presentinvention. The processor 1410 may be configured to generate the trafficrouting criterion evaluation result and report the generated trafficrouting criterion evaluation result. The processor 1410 may beconfigured to decide the routing or not based on the traffic routingcriterion evaluation result. The processor 1410 is configured to processthe traffic through the 3GPP access network and/or the non-3GPP accessnetwork. The processor 1410 may be configured to perform the embodimentof the present invention described with reference to FIGS. 10 to 13.

The RF unit 1430 is connected with the processor 1410 to transmit and/orreceive a radio signal. The RF unit 1430 may include one or more RFunits for 3GPP based access network communication and non-3GPP basedaccess network communication.

The processor may include an application-specific integrated circuit(ASIC), different chip sets, a logic circuit, and/or a data processingapparatus. In FIG. 14, it is illustrated that the single processor 1410is configured to control and manage all RF units for each access networkcommunication, but the wireless apparatus according to the presentinvention is not limited thereto. An embodiment in which the respectiveRF units for each access network communication are functionally coupledwith the respective processors may be available.

The memory 1420 may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother storage device. The RF unit 1430 may include a baseband circuitfor processing the radio signal. When the exemplary embodiment isimplemented by software, the aforementioned technique may be implementedby a module (a process, a function, and the like) performing theaforementioned function. The module may be stored in the memory 1420 andexecuted by the processor 1410. The memory 1420 may be present inside oroutside the processor 1410 and connected with the processor 1410 byvarious well-known means.

In the aforementioned exemplary system, methods have been describedbased on flowcharts as a series of steps or blocks, but the methods arenot limited to the order of the steps of the present invention and anystep may occur in a step or an order different from or simultaneously asthe aforementioned step or order. Further, it can be appreciated bythose skilled in the art that steps shown in the flowcharts are notexclusive and other steps may be included or one or more steps do notinfluence the scope of the present invention and may be deleted.

What is claimed is:
 1. A method for communicating carried out by aterminal in a wireless communication system supporting a multiple accessnetwork, the method comprising: receiving a traffic routingconfiguration from a first access network, the traffic routingconfiguration specifying a traffic routing criterion for routing andprocessing traffic; searching a second access network to discover asecond access network entity, wherein the second access network issearched by receiving at least one beacon frame transmitted from thesecond access network, wherein the beacon frame includes an identifierof the second access network and system information for operating thesecond access network, and wherein the system information included inthe beacon frame comprises load information indicating a load level ofthe second access network; performing traffic routing evaluationdetermining whether the second access network entity satisfies thetraffic routing criterion; reporting a routing evaluation result to thefirst access network when the traffic routing criterion is satisfied,wherein the routing evaluation result includes all of the identificationinformation indicating at least one entity satisfying the trafficrouting criterion among at least one of a plurality of entities of thesecond access network, channel information of the at least one entitysatisfying the traffic routing criterion, and information on the firstaccess network traffic, and wherein the reporting of the routingevaluation result is delayed after the traffic routing criterion issatisfied such that traffic routing evaluation can be performed for allaccess networks including the plurality of entities of the second accessnetwork; receiving a traffic routing indication from the first accessnetwork; and processing the traffic based on the traffic routingindication, wherein, when the traffic routing indication indicates thattraffic of the first access network is processed through the secondaccess network, in the processing of the traffic based on the trafficrouting indication, the traffic of the first access network is processedthrough the second access network, and wherein the second access networkentity indicated by the traffic routing indication is selected by thefirst access network among the plurality of entities of the secondaccess network indicated by the identification information of therouting evaluation result.
 2. The method of claim 1, wherein: thetraffic routing indication indicates the second access network entityfor processing the traffic of the first access network, and the trafficof the first access network is processed by the second access networkentity indicated by the traffic routing indication.
 3. The method ofclaim 2, wherein the traffic routing indication further includes: anidentifier indicating the second access network entity, and trafficinformation on traffic of which processing through the second accessnetwork entity is permitted.
 4. The method of claim 3, wherein thetraffic information includes a radio bearer identifier list associatedwith the traffic of which processing through the second access networkentity is permitted.
 5. The method of claim 4, wherein the processing ofthe traffic of the first access network includes processing the trafficindicated by the traffic information of the traffic routing indicationamong the traffic of the first access network through the second accessnetwork entity.
 6. The method of claim 1, wherein the information on thefirst access network traffic includes a radio bearer identifier listassociated with the first access network traffic.
 7. The method of claim1, wherein the traffic routing configuration includes a routing entitylist including the second access network entity in which the trafficprocessing of the first access network is permitted.
 8. The method ofclaim 7, wherein the performing of the traffic routing evaluationincludes deciding, when the second access network entity discovered bythe search is included in the routing entity list, that thecorresponding second access network entity satisfies the traffic routingcriterion.
 9. The method of claim 1, further comprising: reporting aresult of the traffic processing of the first access network to thefirst access network.
 10. The method of claim 9, further comprising:releasing a radio resource control (RRC) connection with the firstaccess network after reporting the first access network trafficprocessing result.
 11. The method of claim 9, further comprising:receiving traffic processing confirmation from the first access networkas a response to the first access network traffic processing resultreporting; and releasing the RRC connection with the first accessnetwork when the traffic processing confirmation indicates that thefirst access network traffic is normally processed.
 12. The method ofclaim 1, wherein when the traffic routing indication indicates thattraffic of the second access network is processed through the firstaccess network, the processing of the traffic based on the trafficrouting indication includes processing the traffic of the second accessnetwork through the first access network.
 13. The method of claim 1,wherein: the first access network is a 3rd generation partnershipproject (3GPP) based access network, and the second access network is awireless local area network (WLAN) based access network.
 14. A wirelessapparatus that operates in a wireless communication system, the wirelessapparatus comprising: a first radio frequency (RF) unit configured totransmit and receive a first access network signal; a second RF unitconfigured to transmit and receive a second access network signal; and aprocessor that operates in functional combination with the first RF unitand the second RF unit, wherein the processor is configured to: receivea traffic routing configuration from a first access network, the trafficrouting configuration specifying a traffic routing criterion for routingand processing traffic, search a second access network to discover asecond access network entity, wherein the second access network issearched by receiving at least one beacon frame transmitted from thesecond access network, wherein the beacon frame includes an identifierof the second access network and system information for operating thesecond access network, and wherein the system information included inthe beacon frame comprises load information indicating a load level ofthe second access network, perform traffic routing evaluationdetermining whether the second access network entity satisfies thetraffic routing criterion, report a routing evaluation result to thefirst access network when the traffic routing criterion is satisfied,wherein the routing evaluation result includes all of the identificationinformation indicating at least one entity satisfying the trafficrouting criterion among at least one of a plurality of entities of thesecond access network, channel information of the at least one entitysatisfying the traffic routing criterion, and information on the firstaccess network traffic, and wherein the reporting of the routingevaluation result is delayed after the traffic routing criterion issatisfied such that traffic routing evaluation can be performed for allaccess networks including the plurality of entities of the second accessnetwork, receive a traffic routing indication from the first accessnetwork, and process the traffic based on the traffic routingindication, wherein, when the traffic routing indication indicates thattraffic of the first access network is processed through the secondaccess network, the processing of the traffic based on the trafficrouting indication includes the traffic of the first access networkthrough the second access network, and wherein the second access networkentity indicated by the traffic routing indication is selected by thefirst access network among the plurality of entities of the secondaccess network indicated by the identification information of therouting evaluation result.